n8n Expression Syntax

Expert guide for writing correct n8n expressions in workflows.

Expression Format

All dynamic content in n8n uses double curly braces:

Examples:

Core Variables

$json - Current Node Output

Access data from the current node:

$node - Reference Other Nodes

Access data from any previous node:

Important:

• Node names must be in quotes
• Node names are case-sensitive
• Must match exact node name from workflow

$now - Current Timestamp

Access current date/time:

$env - Environment Variables

Access environment variables:

🚨 CRITICAL: Webhook Data Structure

Most Common Mistake: Webhook data is NOT at the root!

Webhook Node Output Structure

Correct Webhook Data Access

Why: Webhook node wraps incoming data under .body property to preserve headers, params, and query parameters.

Common Patterns

Access Nested Fields

Reference Other Nodes

Combine Variables

When NOT to Use Expressions

❌ Code Nodes

Code nodes use direct JavaScript access, NOT expressions!

❌ Webhook Paths

❌ Credential Fields

Validation Rules

1. Always Use {{}}

Expressions must be wrapped in double curly braces.

2. Use Quotes for Spaces

Field or node names with spaces require bracket notation:

3. Match Exact Node Names

Node references are case-sensitive:

4. No Nested {{}}

Don't double-wrap expressions:

Common Mistakes

For complete error catalog with fixes, see COMMON_MISTAKES.md

Quick Fixes

Working Examples

For real workflow examples, see EXAMPLES.md

Example 1: Webhook to Slack

Webhook receives:

In Slack node text field:

Example 2: HTTP Request to Email

HTTP Request returns:

In Email node (reference HTTP Request):

Example 3: Format Timestamp

Data Type Handling

Arrays

Objects

Strings

Numbers

Advanced Patterns

Conditional Content

Date Manipulation

String Manipulation

Debugging Expressions

Test in Expression Editor

1. Click field with expression
2. Open expression editor (click "fx" icon)
3. See live preview of result
4. Check for errors highlighted in red

Common Error Messages

"Cannot read property 'X' of undefined" → Parent object doesn't exist → Check your data path

"X is not a function" → Trying to call method on non-function → Check variable type

Expression shows as literal text → Missing {{ }} → Add curly braces

Expression Helpers

Available Methods

String:

• .toLowerCase(), .toUpperCase()
• .trim(), .replace(), .substring()
• .split(), .includes()

Array:

• .length, .map(), .filter()
• .find(), .join(), .slice()

DateTime (Luxon):

• .toFormat(), .toISO(), .toLocal()
• .plus(), .minus(), .set()

Number:

• .toFixed(), .toString()
• Math operations: +, -, *, /, %

Best Practices

✅ Do

• Always use {{ }} for dynamic content
• Use bracket notation for field names with spaces
• Reference webhook data from .body
• Use $node for data from other nodes
• Test expressions in expression editor

❌ Don't

• Don't use expressions in Code nodes
• Don't forget quotes around node names with spaces
• Don't double-wrap with extra {{ }}
• Don't assume webhook data is at root (it's under .body!)
• Don't use expressions in webhook paths or credentials

Related Skills

• n8n MCP Tools Expert: Learn how to validate expressions using MCP tools
• n8n Workflow Patterns: See expressions in real workflow examples
• n8n Node Configuration: Understand when expressions are needed

Summary

Essential Rules:

1. Wrap expressions in {{ }}
2. Webhook data is under .body
3. No {{ }} in Code nodes
4. Quote node names with spaces
5. Node names are case-sensitive

Most Common Mistakes:

• Missing {{ }} → Add braces
• {{$json.name}} in webhooks → Use {{$json.body.name}}
• {{$json.email}} in Code → Use $json.email
• {{$node.HTTP Request}} → Use {{$node["HTTP Request"]}}

For more details, see:

• COMMON_MISTAKES.md - Complete error catalog
• EXAMPLES.md - Real workflow examples

Need Help? Reference the n8n expression documentation or use n8n-mcp validation tools to check your expressions.